Grayite is a rare thorium phosphate mineral that typically occurs as small crystals in pegmatitic environments. Due to its radioactive and toxic nature, it is primarily sought after by advanced mineral collectors and researchers studying phosphate species.

Hardness

3-4

Mohs

Luster

Resinous to waxy

Streak

White

Transparency

Semitransparent

mineralrarePhosphate Mineral family

Grayite

Hardness: 3-4
Luster: Resinous to waxy
Streak: White
Transparency: Semitransparent

Is this grayite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch grayite with a known reference. Grayite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: resinous to waxy.
4
Match the color range
Compare against the expected color range: light yellow, reddish brown.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: aggregates, cryptocrystalline.

Often confused with

Grayite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Monazite

Mohs 5-5.5

How to tell apart: Monazite is the harder of the two (Mohs 5-5.5 vs. 3-4).

How to tell apart: Luster reads resinous to waxy on Grayite and vitreous on Xenotime.

Compare →

Often found alongside grayite

Minerals reported to co-occur with grayite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (Th,Pb,Ca)(PO₄)·H₂O
Mohs hardness: 3-4
Density: 3.7-4.3 g/cm³
Colors: Light yellow Reddish brown
Streak: White
Luster: Resinous to waxy
Transparency: Semitransparent
Crystal system: Hexagonal
Crystal habit: Aggregates, cryptocrystalline
Cleavage: None
Rarity: Rare
Uses: Collector, Scientific research
Host rock: In a lithium-bearing pegmatite (Mtoko district, Zimbabwe); in an oxidized granitic vein in Precambrian rocks (Gunnison, Colorado, USA); in fracture fillings and disseminated through limestone (Fremont Co., Wyoming, USA)

Where rockhounds find grayite

Classic worldwide localities

Southwest of Gunnison, Gunnison Co., Colorado, USA
Fremont Co., Wyoming, USA
Zapot pegmatite, 25 km northeast of Hawthorne, Fitting district, Mineral Co., Nevada, USA
Havey quarries, Topsham, Sagadahoc Co., Maine, USA
Gooddays mine, Mtoko district, and on the Mahaka and Verdale claims, Wedza district, Zimbabwe
Mungenyi pegmatite, about 65 km southwest of Mbarara, Ankole district, Uganda

Field-hunting tip

Where it forms: In a lithium-bearing pegmatite (Mtoko district, Zimbabwe); in an oxidized granitic vein in Precambrian rocks (Gunnison, Colorado, USA); in fracture fillings and disseminated through limestone (Fremont Co., Wyoming, USA). If you start seeing thorite, monazite-, xenotime- in float, you are in the right ground. Typical habit: aggregates, cryptocrystalline. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify grayite?+

Mohs hardness is 3-4. Luster: resinous to waxy. The streak is white. Common colors include light yellow, reddish brown.

Where is grayite found?+

Notable localities include Southwest of Gunnison, Gunnison Co., Colorado, USA; Fremont Co., Wyoming, USA; Zapot pegmatite, 25 km northeast of Hawthorne, Fitting district, Mineral Co., Nevada, USA; Havey quarries, Topsham, Sagadahoc Co., Maine, USA; Gooddays mine, Mtoko district, and on the Mahaka and Verdale claims, Wedza district, Zimbabwe.

Is grayite safe to handle?+

Grayite contains lead and uranium or thorium and calls for real care. Contains thorium, which is radioactive, and lead, which is toxic if ingested or inhaled as dust; handle with care and keep stored in an appropriate lead-lined container or away from long-term exposure areas.

What rocks look like grayite?+

Grayite is most often confused with Monazite, Xenotime. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with grayite?+

Grayite commonly co-occurs with Thorite, Monazite-, Xenotime-, Zircon. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does grayite form in?+

Where it forms: In a lithium-bearing pegmatite (Mtoko district, Zimbabwe); in an oxidized granitic vein in Precambrian rocks (Gunnison, Colorado, USA); in fracture fillings and disseminated through limestone (Fremont Co., Wyoming, USA). Working float back to the host body is the standard way to chase a fresh occurrence.

What is grayite used for?+

Grayite is used in collector, scientific research.

Find grayite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.